The US Ambassador to Guatemala, John R Hamilton, described the attack as "violent and barbaric" and called on the country's government to investigate and prosecute the perpetrators to the fullest extent of the law.

The armed assailants, Mr Zamora said, posed as investigators from the public prosecutor's office to force their way into his home.

They tied him and his family up, stripped and blindfolded him, kicked two of his sons in the chest and put a gun to his head and threatened him.

Members of the gang were carrying shotguns and apparently receiving orders by phone, Reuters news agency reports.

Attack on media

Ambassador Hamilton said the assault was a blow, not only to Mr Zamora, but also to all journalists in Guatemala.

"It is an imperative and fundamental part of democracy that all journalists practice their profession free from threats, intimidation, and violence," he said.

Guatemala holds a presidential election this November

"Those who would crush freedom of speech will find that there are many brave voices, in addition to Zamora's, who will continue to report in the newspapers, on radio and on television.

"Their persistence is the ultimate proof of the senselessness and futility of such cowardly aggression."

Mr Zamora's newspaper, El Periodico, has been a constant thorn in the side of the government of President Alfonso Portillo Cabrera, continually highlighting alleged corruption by top officials.

In November 2002, government auditors moved into El Periodico's offices to carry out an investigation following the publication of an article which linked the Portillo government with the mafia.

Mr Zamora claimed it was benefiting from funds raised through drug-trafficking, kidnapping and extortion.

His report drew lines between the leaders of organised crime and some government and military heads.

Appeal to president

Following that action by government auditors, the World Association of Newspapers (Wan) wrote to President Portillo reminding him that it was the duty of the state to provide an environment in which journalists and publishers were able to carry out their professional duties without fear of harassment.

Wan said that such incidents fostered a climate of apprehension which could inhibit journalistic investigation and promote self-censorship.

"We respectfully call on you to ensure that any campaign to discredit the independent press that might exist is immediately halted," the body said.

"We also urge you to do everything in your power to ensure that El Periodico, Mr Zamora and other members of the independent media are treated fairly by all members and departments of the government.

"We respectfully ask that you do your utmost to ensure that Guatemala fully respects its constitutional and international commitments to freedom of expression."

El Periodico is currently working on an online version of the newspaper which its editor, Mr Zamora, sees as an "insurance policy for press freedom".

His view is that it will be harder to attempt to silence the independent newspaper if its words are being read globally, rather than just within the country borders of Guatemala.